conversas-mes-chart.html

<div>
    <div style="display: block">
        <canvas baseChart [datasets]="chartData" [labels]="chartLabels" [options]="chartOptions"
                [legend]="showChartLegend" [chartType]="chartType" (chartHover)="chartHovered($event)" (chartClick)="chartClicked($event)">
        </canvas>
    </div>
</div>

conversas-mes-chart.ts

import {Component, Input, OnInit} from '@angular/core';
import { HttpClient } from '@angular/common/http';
import moment from 'moment';
import { Usuario } from '../../models/Usuario';
import { InformationServiceProvider } from "../../providers/information-service/information-service";
import "rxjs/add/operator/map";

@Component({
    selector: 'conversas-mes-chart',
    templateUrl: 'conversas-mes-chart.html'
})
export class ConversasMesChartComponent implements OnInit
{
    // Para que este componente receba dados do componente pai
    // @Input() usuario: Usuario;
    usuario: Usuario;

    // Chart
    public chartOptions = { scaleShowVerticalLines: false, responsive: true };
    public chartType: string = 'bar';
    public showChartLegend: boolean = false;
    public chartLabels: string[] = [];
    public chartData: any[] = [];
    // public chartLabels: string[] = ['Jan', 'Fev'];
    // public chartData: any[] = [{ data: [12, 30] }];

    constructor(private _http: HttpClient, private _informationService: InformationServiceProvider)
    {
        this.usuario = this._informationService.getUsuarioLogado();
    }

    ngOnInit()
    {
        this.getChartDataFromApi();
    }

    getChartDataFromApi()
    {
        console.log('getChartDataFromApi');
        this._http.post(
            'http://localhost:3000/api/statistics/conversations',
            {
                filters:
                    {
                        data_ini: moment().subtract(1, 'months').format('YYYY-MM-DD'),
                        data_fim: moment().format('YYYY-MM-DD'),
                        filtrarPorMes: true
                    }
            },
            {
                headers: {
                    'Content-Type': 'application/json',
                    'Authorization': 'TfI3zgIXHfdSuN1SAgQtW2wDve2SFZcjEF9sHPZRtcz'
                }
            }
        )
            .subscribe(
                (response) => {
                    this.assembleChartData(response);
                },
                (erro) => {
                    console.log('Deu erro');
                }
            );
    }

    assembleChartData(data)
    {
        if (data.length > 0)
        {
            let dataArray = [];
            var io = [];

            for (let i = 0; i < data.length; i++)
            {
                data[i]._id.mes = this.changeMonthName(data[i]._id.mes);

                this.chartLabels[i] = data[i]._id.mes + '/' + data[i]._id.ano;
                io[i] = data[i]._id.mes + '/' + data[i]._id.ano;
                dataArray[i] = data[i].count;
            }

            this.chartData = [ { data: dataArray } ];
        }
    }

    changeMonthName(month)
    {
        switch (month)
        {
            case '01':
                return 'Jan';
            case '02':
                return 'Fev';
            case '03':
                return 'Mar';
            case '04':
                return 'Abr';
            case '05':
                return 'Mai';
            case '06':
                return 'Jun';
            case '07':
                return 'Jul';
            case '08':
                return 'Ago';
            case '09':
                return 'Set';
            case '10':
                return 'Out';
            case '11':
                return 'Nov';
            case '12':
                return 'Dez';
        }
    }

    // events
    public chartClicked(e:any):void
    {
        console.log(e);
    }

    public chartHovered(e:any):void
    {
        console.log(e);
    }
}

Erro

TypeError: Cannot read property 'data' of undefined
    at BaseChartDirective.Array.concat.BaseChartDirective.updateChartData (http://localhost:8100/build/0.js:19478:24)
    at BaseChartDirective.Array.concat.BaseChartDirective.ngOnChanges (http://localhost:8100/build/0.js:19428:26)
    at checkAndUpdateDirectiveInline (http://localhost:8100/build/vendor.js:12445:19)
    at checkAndUpdateNodeInline (http://localhost:8100/build/vendor.js:13951:20)
    at checkAndUpdateNode (http://localhost:8100/build/vendor.js:13894:16)
    at debugCheckAndUpdateNode (http://localhost:8100/build/vendor.js:14766:76)
    at debugCheckDirectivesFn (http://localhost:8100/build/vendor.js:14707:13)
    at Object.eval [as updateDirectives] (ng:///ConversasMesChartModule/ConversasMesChartComponent.ngfactory.js:36:9)
    at Object.debugUpdateDirectives [as updateDirectives] (http://localhost:8100/build/vendor.js:14692:21)
    at checkAndUpdateView (http://localhost:8100/build/vendor.js:13861:14)